Make qglobal.h complain if you use -fPIE

Prior to Qt 5.4.2 (commit 36d6eb721e7d5997ade75e289d4088dc48678d0d), we
allowed it, but now we need to enforce that it is not used. Note that
-fPIE does define __PIC__, so we need this to catch the use of -fPIE.

[ChangeLog][Important Behavior Changes] On x86 and x86-64 systems with
ELF binaries (especially Linux), due to a new optimization in GCC 5.x in
combination with a recent version of GNU binutils, compiling Qt
applications with -fPIE is no longer enough. Applications now need to be
compiled with the -fPIC option if Qt's option "reduce relocations" is
active. Note that Clang is known to generate incompatible code even with
-fPIC if the -flto option is active.

Task-number: QTBUG-45755
Change-Id: I66a35ce5f88941f29aa6ffff13dd210e0aa2728f
Reviewed-by: Dmitry Shachnev <mitya57@gmail.com>
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/dist/changes-5.4.2 b/dist/changes-5.4.2
index e1ad9b6846..5827187e9e 100644
--- a/dist/changes-5.4.2
+++ b/dist/changes-5.4.2
@@ -34,6 +34,13 @@ information about a particular change.
   common EXIF-format (big-endian) was not working until 5.4.1. 5.4.2 restores the
   behavior of 5.4.0 and earlier for most EXIF-tagged JPEGs.
   EXIF orientation will be an opt-in starting with Qt 5.5.
+- On x86 and x86-64 systems with ELF binaries (especially Linux), due to
+  a new optimization in GCC 5.x in combination with a recent version of
+  GNU binutils, compiling Qt applications with -fPIE is no longer
+  enough. Applications now need to be compiled with the -fPIC option if
+  Qt's option "reduce relocations" is active. Note that Clang is known
+  to generate incompatible code even with -fPIC if the -flto option is
+  active.
 
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